0 Assigned ID: 6810 ----- Attempting Submission 1 (Thu Apr 10 22:58:50 GMT 2025) ----- HST Phase I Proposal 6810 successfully submitted. Receipt: # 6810-1 ----- Attempting Submission 2 (Thu Apr 10 23:49:50 GMT 2025) ----- Version 1 - August 8, 2025 Version 2 - September 5, 2025 --- longer exposures per orbit, removed post flash, new 2-point dither pattern and pos targs between orbits (based on the 3 point dither pattern) Version 3 - September 12, 2025 --- new pos targs of (+1.5,-1.5) pixels and (-2.33, +1.5) pixels -2098752463 ----- Attempting Submission 1 (Fri Aug 08 18:46:14 GMT 2025) ----- ----- Attempting Submission 2 (Fri Sep 05 20:27:05 GMT 2025) ----- ----- Attempting Submission 3 (Fri Sep 12 11:48:12 GMT 2025) ----- We have discovered a remarkable star-forming Brightest Cluster Galaxy (BCG) at spectroscopic redshift of z=0.81 that has asymmetric and extended dust emission over 30 kiloparsecs, embedded with a powerful radio source. BCGs are the most massive galaxies in the Universe, at any epoch, and reside at the centers of galaxy clusters. Besides their inherent interest as extreme systems, BCGs undergo an astrophysical balancing act between gas cooling and energy feedback within the dense intracluster medium. They thus offer a unique opportunity to study the physics of AGN feedback, as the energy imparted by the AGN leaves unique imprints on the surrounding gaseous medium. We propose joint HST UV and JVLA imaging to map out recent star formation and search for jetted AGN emission. We will complement this with high-resolution archival ALMA dust continuum and optical Euclid observations for a premiere case study of a star-forming and radio-bright BCG. The full suite of observations will allow us to connect the origin of the dust tail to the radio source and investigate the role of feedback in this cluster core at z=0.81. The goal of this program is to obtain 3 orbits of WFC3/UVIS imaging over a galaxy cluster at z=0.8 in a single filter F475W. The cluster extends beyond the full FOV, so the full detector will provide useful ancillary data, but the primary target of interest is the brightest cluster galaxy (BCG). The BCG main lobe is 1.5 arcesc in diameter, but it also has a dust tail which extends over 6 arcsec to the east, and potential jetted radio emission over 16 arcsec, aligned along the dust tail. The primary aim of the F475W imaging is to trace clumpy and filamentary emission (rest-frame 260nm), roughly down to levels of ~4 Msol/yr, within the dust tail and in the vicinity of the BCG and radio emission. We aim to achieve this over 3 orbits in F475W. We are also getting joint VLA imaging at high-resolution with this program. We do not place orient constraints to maximize schedulability, but aim to place the BCG at the optimal detector position to maximize it's S/N and mitigate CTE losses, which could be especially important for fainter UV clumps along the dust tail. Orbit / visit / dithering strategy: ----------------- The single visit consists of 3 orbits, all with F475W. We will use a standard 2-point dither pattern within each orbit to facilitate PSF reconstruction and cosmic ray removal (WFC3-UVIS-DITHER-LINE-2PT). We will thus acquire two individual exposures per orbit, at ~1220 seconds each. Given the long exposures, we expect the background to be high enough that we will not require a postflash to help mitigate CTE losses. We have also included small pos targ offsets of +1.5, -1.5 pixels and -2.33, +1.5 pixels from the first orbit to help with cosmic ray removal over the 6 dithered exposures. Aperture: --------------- We will place the BCG at the reference position of aperture UVIS2-C1K1C-CTE. We will stil read out the full 2-chip frame to gain coverage of the surrounding cluster field, but will minimize CTE losses of the BCG and dust tail by placing them closer to the readout amplifier. Given the extent of the dust tail and radio emisison over 16 arcsec, there should be ample space to still cover these features in full for any orient. Our team consists of core members of the SpARCS collaboration and are all experts in multiwavelength observations of high-redshift galaxies, galaxy clusters and Brightest Cluster Galaxies. All senior investigators have previously been the PI or Co-I on successful HST programs. Dr. Allison Noble is an expert on galaxy evolution and formation, protocluster studies, and BCG evolution, focusing particularly on molecular gas in high-redshift galaxies. She has led multiple proposals on ALMA and HST, and is PI of the dust continuum ALMA program from which the target is drawn. Dr. Tracy Webb is an expert on Brightest Cluster Galaxies and their star formation, as well as dusty starburts. She is the PI of an ALMA CO program onn BCGs. She has extensive experience with SpARCS-1049, another high-redshift BCGs that seems to be the result of runaway cooling of the gas in the absence of an AGN. Dr. Julie Hlavacek-Larrondo led the JVLA and X-ray observations of SpARCS-1049, and is an expert in AGN feedback, jets, and X-ray cavities. Dr. Esra Bulbul is a member of the eROSITA collaboration and is an expert on ICM studies and galaxy cluster surveys in the X-ray. Drs. Gillian Wilson and Adam Muzzin are the PIs of the Spitzer Adaptation of the Red Sequence Cluster Survey (SpARCS), from which the proposal target is drawn and have strong backgrounds in optical/UV observations. Graduate student Simon Mork has been leading the effort in searching for archival data on SpARCS 0333 and has extensive experience with galaxy clusters in optical surveys and SED fitting. He will be leading the analysis and working with all the co-Is to gain expertise on the joint observations. Graduate student Alex Pigarelli is an expert on molecular gas studies in high-redshift clusters and HST image analysis. He will work with PI Noble and graduate student Mork on the HST portion of the data analysis. Dr. Patrick Kamieneski is an expert on dusty star-forming galaxies. Galaxies Supermassive Black Holes and Active Galaxies 6 false true false false false false true PRIMARY 12 true SUPPORTED GALAXY COOLING FLOW HIGH REDSHIFT GALAXY JET TIDAL TAIL YES J2000 J2000 WFC3/UVIS Imaging No No F475W POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 1 false 1757677556811 The scheduling data was generated by CASM 33.1. 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